Takes the provided list of messages, transforms them, passes the
transformed list on to the next transformation (if any) and then returns
the resulting list of message parts after all of the transformations have
been applied.

validateRsv

Validates the RSV and opcode combination (assumed to have been extracted
from a WebSocket Frame) for this extension. The implementation is
expected to unset any RSV bits it has validated before passing the
remaining RSV bits to the next transformation in the pipeline.

validateRsvBits

Validate that the RSV bit(s) required by this transformation are not
being used by another extension. The implementation is expected to set
any bits it requires before passing the set of in-use bits to the next
transformation.

Takes the provided list of messages, transforms them, passes the
transformed list on to the next transformation (if any) and then returns
the resulting list of message parts after all of the transformations have
been applied.